Removal of carbonaceous deposits



Patented Apr. 1947 REMOVAL OF CARBONACEOUS DEPOSITS Franz A. Horsley,Martinez, CaliL, assignor to Shell Development Company, San Francisco,Calif., a corporation of Delaware I No Drawing. Application March 6,1944, Serial No. 525,326

12 Claims. (01. 134-27) 1' 2 The present invention relates to a methodfor within the interstices of the carbonaceous deposremoving undesirablecarbonaceous deposits and its. Other objects, together with some of themore particularly to a method for removing acidic advantages to bederived in utilizing the present carbonaceous deposits from heatingtubes and invention, will become apparent from the follow- 1 the like. 5ing detailed description.

In numerous industrial processes, carbon con- According to the presentinvention, it has been taining materials are treated by. heating or infound that carbonaceous deposits may be removed other ways in a mannerconducive to the formafrom surfaces to which they are adhering by tionof coke or similar carbonaceous deposits generating carbon dioxide gaswithin the interupon various surfaces within the treating equipstices ofthe coating. This may be generally ment. 'I'hesedeposits are almostinvariably obbrought about by reaction between an aqueous v jectionableand in many instances deleterious. In carbonate solution and an aqueousacid solution the past it has been common practice to remove within theinterstices of the carbonaceous deposit] carbonaceous deposits of thisnature mechanipreferably by first impregnating the deposit with cally,i. e., either by means of special cutting an acid solution and then witha carbonate soluequipment which may be inserted into the equiption. 4ment which it is desired to clean or by partially For purposes ofillustration, the invention-will dismantling the'equipment to gainaccess to the be described with reference to the removal of parts whichare coated. Mechanical cleaning carbonaceous deposits from the heatingtubes of procedure for the removal ofcarbonaceous dean acidconcentrator. The conventional acid conposits is, however, excessivelytime consuming centrator comprises a large steel container near andnecessitates long and undesirable periods of the bottom of which aredisposed heating coils inoperation of the equipment during cleaning.through which steam or hot oil may be passed.

Further, there is the constant danger of dam- When concentrating certaintypes of dilute acid, age to the equipment by mechanical cleaners or asfor examp e Spent Sulfuric acid derived fIOm during the dismantling andreassembling operpetroleum refining processes, the organic impuriations,ties contained the-sacid carbonize and a thin Attempts have also beenmade to clean surfilm of carbon i's'tieposited on the heating tubes.faces upon which carbonaceous deposits occur by The laminated depositwhich is gradually built other than mechanical means, as for example byup as successive batches of acid are concentrated burning the carbon outwith an oxygen stream eventually attains sufficient thickness toseriously orby treating the carbonaceous deposits with" interfere withthe heat transfer through the heatstrong chemical reagents which willconvert the in t s- The conventional t d 0f an n carbon to carbondioxide. These methods} have the carbonaceous deposits from these tubesinalso been found to be generally undesirable due volves removal of thetubes and scrap and to ineffective removal of the objectionabledeposrequires that the concentrator be out of operaits, attack on themetal partsby the chemical tion for a period O at least pp m yreagentsor as a result of damage to the equiphours. ment as a consequence ofoverheating during The following procedure was carried out in lieu theburning operation. of the dismantling and scraping operations. The It isan object of the present invention .toiiroconcentrator was drained and600 gallons of water vide a method for rapidly and effectivelyremovintroduced as a flushin m d to m ve ccuing carbonaceous depositsfrom surfaces to which mulations of acid on the floor of theconcentrathey are adhering. Another object is to provide tor. Theflushing Wat r was t en drained out a method for carrying out theremoval of such and approxim ly 7 ll of an aqu deposits withoutnecessitating dismantling of solution containing approximately 5% byweight equipment which may contain internal deposits. of sodiumbicarbonate introduced, filling the con- A further object is to providea method for recentrator to a level about 10 inches above the movingcarbonaceous deposits from the interior heatin tu s- The bicarbonateSolution W surfaces of equipment in a form suitable for heated to andmaintained at the boiling point facile removal from the equipment andwithfor approximately 30 minutes, after which it was out danger ofdamage to the surfaces of the equipdrained and the bottom of theconcentrator again ment. Still another object is to provide a methodflushed with approximately 600 gallons of water. for removingcarbonaceous deposits from surfaces T e concentrator wa then charged w hSpent to which they are adhering by gas generation 5 sulfuric acid andthe heat transfer rate was found to be as good as when the concentratorwas first used. The total time required for the described cleaningprocedure was less than 4 hours. Upon examination, it was found that thecarbonaceous deposits had been completely removed from the tubes.

In the above example the carbonaceous deposits were,- of course,impregnated with acid as rapidly as they formed. However, in thoseinstances wherein a neutral deposit is encountered, an acid treatmentshould be applied before subjecting the deposits to the action of thecarbonate solution. Alternatively, the neutral deposit may be firstimpregnated with a carbonate solution and then subjected to the actionof an acid stronger than carbonic acid. In either case, it appears thatthe resulting reaction between the acidic and carbonate solutionsproduces carbon dioxide within the interstices of the carbonaceousdeposits and the carbon dioxide breaks ofi the carbonaceous depcsitsfrombeneath in escaping. It will thus be apparent that any combination maybe utilized which will react to yield carbon dioxide.

Particularly suitable sources of carbon dioxide for the purposes of thepresent invention are aqueous solutions of the inorganic alkalicarbonates, e. g.,s odiurn, potassium and ammonium solubility in water.However, other less water soluble inorganic carbonates may be employedun der special conditions, as for example, the solubility of manyinorganic carbonates inwater may be substantially increased by passingcarbon dioxide gas through the water while dissolving the carbonates andlei-carbonates. These compounds are preferred because of theirrelatively great over the carbonate solution. Examples of specificcompounds which may be employed in solution under conditions describedabove are the carbonatesof lithium, beryllium, magnesium, calcium,barium, zinc, lead, manganese, silver, etc. In many instances it willalso be found satisfactory to employ slurrys or suspensions of the moreinsoluble carbonates in water, or alternatively, al-. '1' coholicsolutions, slurrys or suspensions of these compounds.

Any acid preferably in dilute aqueous solution I which is stronger thancarbonic acid and which I will react with the carbonates to producecarbon 1 dioxide may be utilized, as forex'ample aqueous solutions ofsulfuric, selenious, hydrochloric, hydrobromic, iodic, nitric,phosphoric, formic, acetic, lactic, oxalic, citric; etc. acids. Thoseacids weaker than acetic acid, i. e. acids having a dissociationconstant less than approximately illare generally unsatisfactory for thepur-'- poses of the invention since the amount of carbon dioxide formedduring the reaction with carbonates is usually insumcient to exceed thesolubility of carbon dioxide in water.

It will be apparent that the process may beff applied in its principlesto the removal of any porous carbonaceous deposits from any surfaces towhich they may be adhering. If other materials are present in thecarbonaceous deposits which will react unfavorably with carbonate ordilute acid solutions, they should be removed by flushing with water oranother suitable solvent before the acid or carbonate solution isintroduced. Improved impregnation of the carbonjet 7 According topreferred procedure, the carbonaceous deposit which it is desired toremove is first subjected to the action of a dilute acid solution, asfor example aqueous sulfuric acid having a concentration between about20% and by weight H2804, for a period of approximately one half hour.The concentration of the acid is not critical, however, and anyconvenient concentration may be employed. Shorter impregnation time mayalso be employed if it is feasible tocarry out the impregnation underreduced pressure. The acid is then drained out of the system and adilute solution of sodium acid carbonate substituted. The concentrationof the carbonate solution may also be selected as a matter ofconvenience, although there appears to be no advantage in utilizingcarbonate solutions having a concentration appreciably in excess of 10%by weight. Heat is preferably. applied during the reaction between thacid and the carbonate in the interstices of the carbonaceous deposit.The carflushed with water and is ready for use again.

The reagents may both be stored, afterfiltration' the carbonatesolution, and reused until exhauste of the carbonaceous matter from Thprocedure outlined above wherein the carbonaceous deposits are firstimpregnated with acid and then with a carbonate solution is gen--,erally preferred in order to minimize possible attack by the acid onmetal surfaces to which the deposits may be adhering during:the'reaction 50.

period, which is usually longer than that required for the initialimpregnation step. Howevezywhen the deposits are present on acidresistant material, they may be'equally well initially impregq notedwith. a carbonate solution andthen sub- .iected to the action of an acidsolution. I

"I claim as my invention:

1.1111 a method for removing-porouscarbonaceous deposits resistant tothe action of Strong, sulfuric acid from surfaces to which theyadhere. 4the interstices ofsaid-deposits containing an acid having a dissociationconstant not lezsth'an'ap-u I proximatelyfifl-" ithe 'stepcomprisingsubjecting- --said deposits to thejactionof aninorganic carbonatesolution and thereby dioxide gaslwithinthe interstices of saidcarbo- 'naceousdeposita; 'j, f 2. In a. method for removing porouscarbonaceous deposits resistant tothe action of strong sulfuric acidfrom surfaces to which they adhere, the interstices of said depositscontaining an acid having a dissociation constant not less thanapproximately 10*, thestep comprising subjecting said deposits to theaction of an inorganic alkali carbonate solution and thereby generatingcarbon generating carbon alkali carbonate solution and therebygenerating carbon dioxide gas within the interstices of'said' sulfuricacid from surfaces to which they adhere,

in the interstices of said carbonaceous deposits.

generated within the interstices of said carboceous deposits resistantto the action of strong sulfuric acid from surfaces to which theyadhere, the interstices of said deposits containing an acid having adissociation constant not less than approximately the step comprisingsubjecting said deposits to the action of a heated inorganiccarbonaceous deposits.

4. In a method for removing porous carbonaceous deposits resistant tothe action-of stron the interstices of said deposits containing sulfuricacid, the step comprising subjecting said deposits to the action of asodium acid carbonate solution and thereby generating carbon dioxide gaswith- 5. In a method for removing porous carbonaceous deposits resistantto the action of strong sulfuric acid from surfaces to which theyadhere, the steps comprising impregnating the interstices of saiddeposits with an acid having a dissociation constant not less thanapproximately 1H and thereafter subjecting said acid impregnated de- 7posits to the action of an inorganic carbonate solution whereby carbondioxide gas is generated "by generating carbon dioxide gas within saidwithin the interstices of said carbonaceous dep sits. I

6. In a method for removing porous carbonaceous deposits resistant tothe action of stron surfuric acid from surfaces to which they adhere,

the steps comprising impregnating the interstices 3 constant not lessthan approximately 10- and thereafter subjecting said acid impregnatedde-. posits to the action of an inorganic alkali car bonate solutionwhereby carbondioxide gas is naceous deposits.

'7'. In-a method for removing porous carbona- I ceous deposits resistantto the action of strongthe comprising subiecting said deposits I I"Lerating carbon dioxide to the action of an aqueous solution containingapproximately 5% by. weight of sodium acid carbonate for a period ofapproximately 30 minutes at a temperature of approximately 100 0.,whereby carbon dioxide gas is generated within the interstices of saidcarbonaceous deposits.

sulfuric acid from surfaces to which they adhere,

the step comprising reacting within the inter-' stices of saidcarbonaceous deposits an inorganic carbonate solution and an acid havinga dissocia tionconstant not iss than approximately 10-,

. thereby generating carbon dioxide gas within said interstices. I I

.10. In a method for removing porous carbonaceous deposits resistant tothe action of strong dissociation constant not less than approximately 71 10", thereby generating carbon dioxide gas within said interstices.

ii. In a method for removing porous carbona= ceous deposits resistant tothe action of strong sulfuric acid from surfaces to which they adhere, Ithe step comprising reacting within'the interstices of said carbonaceousdeposits an inorganic alkali carbonate solution and sulfuric acid,thereinterstices. I I 1 12. In a method tor removing porous carbonaceousdeposits resistant to the action of strong sulfuric acid from surfacesto which they adhere, the step comprising reacting sulfuric acid withsodium acid carbonate solution within the inter sticesof saidcarbonaceous deposits, thereby gengas within said interstices.

FRANZ a. nonsnnr.

I meanness crrm The following references are of. record in the file ofthis patent: I

sulfuric acid from surfaces to which they adhere, I II II the stepscomprising impregnating the interstices i MAW Ptsmm of said depositswith sulfuric acid and thereafter Number Name subjecting saidimpregnated deposits to the ac- 795,2 5 Forster July ts, gene tion of aninorganic alkali carbonate solution. 3, 3 m 1 m. 3 3 j.,. b.v carbondioxide gas is senersted within 1,194,542 Raymond 118.15, iris theinterstices of said'carbonaceous deposits. 54,533 Harvey m a I I 8. Ina. method for removing porous carbonai I ceous deposits resistant tothe. action of strong i: I mama Pfimfi sulfuric acid from'surfaces towhich they adhere, I Number Ccnntrs Eats the interstices of saiddeposits containing sulfuric '56 Ger Aug. 1o.

was

